Question

The crystalline salt $ \text{N}{{\text{a}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{. x}{{\text{H}}_{\text{2}}}\text{O} $ on heating loses 55.5% of its weight the formula of crystalline salt is?
a) $ \text{N}{{\text{a}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{. 5}{{\text{H}}_{\text{2}}}\text{O} $
b) $ \text{N}{{\text{a}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{. 7}{{\text{H}}_{\text{2}}}\text{O} $
c) $ \text{N}{{\text{a}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{. 2}{{\text{H}}_{\text{2}}}\text{O} $
d) $ \text{N}{{\text{a}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{. 10}{{\text{H}}_{\text{2}}}\text{O} $
e) $ \text{N}{{\text{a}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{. 6}{{\text{H}}_{\text{2}}}\text{O} $

Answer 1

Hint: The inorganic chemical sodium sulphate (also known as sodium sulphate or sulphate of soda) and many related hydrates have the formula $ N{{a}_{2}}S{{O}_{4}} $ . All of the forms are white solids that are extremely water soluble. The decahydrate is an important commodity chemical product, with annual output of 6 million tonnes. It is primarily utilised as a filler in powdered home laundry detergents and in the Kraft paper pulping process to produce extremely alkaline sulphides.

Complete answer:
Water molecules contained inside crystals are referred to as water of crystallisation in chemistry. In the production of crystals from aqueous solutions, water is frequently present. The entire mass of water in a substance at a certain temperature is sometimes referred to as water of crystallisation, and it is usually present in a definite ratio. Water contained in the crystalline framework of a metal complex or a salt that is not directly bound to the metal cation is known as "water of crystallisation."
We got $ \mathrm{Na}_{2} \mathrm{SO}_{4} \cdot\left(\mathrm{OH}_{2}\right)_{n} $ where it will be established how many so-called crystallisation waters there are.
We express dehydration reactions as given down .
 $ \mathrm{Na}_{2} \mathrm{SO}_{4} \cdot\left(\mathrm{OH}_{2}\right)_{n}+\Delta \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}+n \mathrm{H}_{2} \mathrm{O} $
We'll suppose we start with a 100g mass of sodium sulphate hydrate, of which 55g are the solvation fluids, and $ 45.5 \cdot g $ are the $ \mathrm{Na}_{2} \mathrm{SO}_{4} $ .
Using the formula $ \text{No}\text{. of moles = }\dfrac{\text{Given mass}}{\text{Molecular mass}} $
Moles of sulfate, $ =\dfrac{45.5 \cdot g}{142.04 \cdot g \cdot m o l^{-1}}=0.317 \cdot \operatorname{mol}(i) $
Moles of waters, $ =\dfrac{54.5 \cdot g}{18.01 \cdot g \cdot m o l^{-1}}=3.03 \cdot $ mol $ (i i) $
To calculate the number of crystallisation waters, divide (ii) by I i.e. there are 10 moles of water per mole of sodium sulphate (or near enough, we rounded up to 10 from 9.5).
And hence we get $ \mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O} $ , the so-called decahydrate as the answer
Anhydrous sodium sulphate is frequently used to treat wet liquids as a first drying agent.

Note:
Glauber's salt, commonly known as mirabilite, is a hydrous sodium sulphate mineral having the formula $ \mathrm{Na}_{2} \mathrm{SO}_{4} \cdot 10 \mathrm{H}_{2} \mathrm{O} $ . It's a vitreous, colourless to white monoclinic mineral that develops when sodium sulfate-bearing brines evaporate. It can be found around saline springs and along the shores of saline playa lakes.